Molecular characterization of H1N1 influenza A viruses from human cases in North America

Subtypes of H1N1 influenza virus can be found in humans in North America,while they are also asso-ciated with the infection of swine.Characterization of the genotypes of viral strains in human popula-tions is important to understand the source and distribution of viral strains.Genomic and protein sequences of 10 isolates of the 2009 outbreak ofinfluenza A(H1N1) virus in North America were obtained from GenBank database.To characterize the genotypes of these viruses,phylogenetic trees of genes PB2,PB1,PA,HA,NP,NA,NS and M were constructed by Phylip3.67 program and N-Linked glycosylation sites of HA,NA,PB2,NS1 and M2 proteins were analyzed online by NetNGlyc1.0 program.Phylogenetic analysis indicated that these isolates are virtually identical but may be recombinant viruses because their genomic fragments come from different viruses.The isolates also contain a char-acteristic lowly pathogenic amino acid motif at their HA cleavage sites(IPSIQSR↓GL),and an E residue at position 627 of the PB2 protein which shows its high affinity to humans.The homologous model of M proteins showed that the viruses had obtained the ability of anti-amantadine due to the mutation at the drug-sensitive site,while sequence analysis of NA proteins indicated that the viruses are still suscep-tible to the neuraminidase inhibitor drug(i.e.oseltamivir and zanamivir) because no mutations have been observed.Our results strongly suggested that the viruses responsible for the 2009 outbreaks ofinfluenza A(H1N1) virus have the ability to cross species barriers to infect human and mammalian animals based on molecular analysis.These findings may further facilitate the therapy and prevention of possible transmission from North America to other countries.